1. Field of the Invention
The present invention relates to a multi-stage rotary compressor, and more particularly, to a multi-stage rotary compressor to reduce a driving load and prevent a malfunction incurred by a steep pressure rising.
2. Description of the Related Art
A multi-stage rotary compressor, as disclosed in Japanese Patent Publication No. 2004-19599 (published on Jan. 22, 2004), includes a lower first compression chamber and an upper second compression chamber. In operation, a refrigerant gas is primarily compressed in the first compression chamber to an intermediate pressure, and secondarily compressed in the second compression chamber to a higher pressure while successively passing through the first and second compression chambers, thereby being discharged into a hermetic casing of the compressor in a substantially high pressure state.
The rotary compressor further includes first and second rollers that eccentrically rotate in the respective compression chambers, first and second vanes each serving to sectionalize an associated one of the compression chambers into a suction space and a discharge space while reciprocating in a radial direction of the associated compression chamber according to a rotation of the first or second roller, and first and second vane springs to press the vanes toward the rollers.
By virtue of the elasticity of the vane springs and the high interior pressure of the hermetic casing, the first and second vanes are kept in close contact with outer circumferences of the first and second rollers, respectively, when they are pressed inward in the respective compression chambers to compress a refrigerant.
However, the above described multi-stage rotary compressor experiences a pressure difference between the interior of the first compression chamber and the interior of the hermetic casing because, during a compression operation, the second compression chamber and the hermetic casing are kept at high interior pressures, whereas the first compression chamber is kept at an intermediate interior pressure below the interior pressure of the hermetic casing. The pressure difference causes the first vane to press the outer circumference of the first roller with an unnecessarily large force, resulting in an increased driving load.
Thereby, although the second vane presses the second roller with a moderate force because there exists no noticeable pressure difference between the second compression chamber and the hermetic casing, the substantial pressure difference between the first compression chamber and the hermetic casing problematically increases a press force of the first vane against the outer circumference of the first roller, resulting in much frictional wear between the first vane and the first roller. Further, the increased driving load incurs a loss of energy.
Another problem of the multi-stage rotary compressor is that the interior pressure of the first compression chamber rises abruptly (i.e. above the intermediate pressure) if a refrigerant liquid is introduced into the first compression chamber during an initial operation. Because the refrigerant, passed by the first compression chamber, is again compressed in the second compression chamber rather than discharged directly into the hermetic casing, the abrupt pressure rising generates an overload in the compressor, hindering a smooth starting thereof.